Fixed the issue #314 where the rectangle selection tool did not work in Obsidian 1.8.
This bug was caused by several reasons, including that the Obsidian team has changed the CSS class name pdf-viewer to pdfViewer in v1.8.0 (I don't know why!).
This might be also impacting some advanced users' custom CSS snippets, so I thought I'd share this discovery here.
Full Changelog: 0.40.15...0.40.16